A common problem experienced by truck operators is the failure of their truck air horns to function properly at low temperatures or when there has been an accumulation of ice and snow on and in the horn. These horns usually must be mounted on the outside of the truck and are thus unavoidably exposed to the elements. Horn failures often occur without warning creating a serious safety problem, since the vehicle operators may only become aware of this malfunction when they are unable to sound the horn to avert an impending collision. Furthermore, even if drivers do become aware of the failure of the truck horn to operate in advance of an emergency situation, they may still be unable to correct the problem in any practical way without halting their trip, thus falling behind schedule and being put to great inconvenience and expense.
The horn malfunctioning is usually due to the freezing of the sounding diaphragm or the accumulation of ice and snow blocking the flow of air through the horn or muffling the horn sound. On ships and trains this problem may be alleviated by powering the horns with hot steam, but this is not available to trucks.